We have a 2003 Vauxhall Zafira Design diesel which we bought secondhand about three years ago. For some time, we have had problems with the management light, which comes on after about 20 mins on the motorway when driving at 70+ mph. This causes the car to lose power and go into 'limp home mode', unless you stop the car and restart it. When we have had the computer read, no problem is ever detected and the car is fine in every other respect. Indeed, on occasions, after servicing, we can go for months without the light coming on. However, it is coming on more frequently at the moment, which makes long motorway journeys very frustrating and potentially dangerous. As I say, the computer has been read when the light is on and it also had a series of tests at a Vauxhall dealer a while ago, and yet no problem has been detected. Can you suggest what the problem might be and what could be done about it?